1. Field of the Invention
The invention is related to the field of magnetic recording disk drive systems and, in particular, to fabricating patterned media by growing laterally ordered arrays of vertical magnetic grains of a recording layer on patterned seed layers.
2. Statement of the Problem
Magnetic hard disk drive systems typically include a magnetic disk, a recording head having write and read elements, a suspension arm, and an actuator arm. As the magnetic disk is rotated, air adjacent to the disk surface moves with the disk. This allows the recording head (also referred to as a slider) to fly on an extremely thin cushion of air, generally referred to as an air bearing. When the recording head flies on the air bearing, the actuator arm swings the suspension arm to place the recording head over selected circular tracks on the rotating magnetic disk where signal fields are written to and read by the write and read elements, respectively. The write and read elements are connected to processing circuitry that operates according to a computer program to implement write and read functions.
In a disk drive utilizing perpendicular recording, data is recorded on a magnetic recording disk by magnetizing the recording layer in a direction perpendicular to the surface of the disk. Typically, the recording layer is a continuous thin film of a magnetic alloy, which naturally forms a random mosaic of nanometer-scale grains, which behave as quasi-independent magnetic elements. As a result, grain boundaries don't always correspond with bit transition boundaries, thus creating an increased noise level. One solution has been to fabricate smaller magnetic grains such that the magnetic transitions between bits become relatively straighter. However, present disk drive technology is reaching its physical limit for recording capacity, because further shrinking the magnetic grain sizes can cause un-stability in their magnetization due to thermal excitations at room temperature, known as the superparamagnetic effect.
Patterned media is one of the solutions which can circumvent the density limitations imposed by the superparamagnetic effect. In patterned media, the magnetic recording layer is created as an ordered array of pre-defined highly uniform islands or cells, each island capable of storing an individual bit. In order to take advantage of patterned media, write synchronization between the write head position and the position of the islands is necessary. While patterned media delays the onset of superparamagnetism, its cost competitive mass fabrication has proved to be challenging. One approach to fabricate patterned media involves depositing the magnetic recording layer onto a substrate, and subsequently patterning the magnetic recording layer. The magnetic recording layer is initially a continuous film, which is then covered with a resist material, and the dimensions of the magnetic islands and trenches separating the magnetic islands are defined using a lithographic process. As a result, flyability is a problem because the finished media has topographical features that affect the aerodynamics of the read/write head. Therefore, additional processes must be performed to planarize the media. A further problem is that it is difficult to use reactive-ion-etching (RIE) to remove portions of the magnetic layer without affecting the magnetism of the remaining magnetic islands (e.g., causing softening, loss of magnetic moment, etc.). While an ion-beam process can be utilized to remove portions of the magnetic layer, this approach is typically too costly for large-scale manufacturing.
A second fabrication approach involves depositing the magnetic recording layer onto a pre-patterned substrate. The pre-patterned substrate defines the islands and trenches, and the magnetic materials cover both the islands and trenches. This approach avoids the difficulty of patterning the magnetic layer itself, but still has the common problem of flyability, and a subsequent planarization process is needed. Additionally, the magnetic material in the trenches creates undesired stray fields, which contribute to high background noise levels during the read back process. Further more, material deposited onto the sidewalls of the islands may cause coupling of adjacent islands to each other via the trenches. Further problems with this fabrication method include uncontrolled overgrowth effects and reduced magnetism due to curving of the media layers at the edge of the islands.